Increased efficiency of the outer membrane PhoE protein pore in escherichia coli K-12 mutants with heptose-deficient lipopolysaccharide

Abstract

The pore properties of PhoE protein channels in the outer membrane of a lipoprotein-deficient mutant and in a mutant with heptose-deficient lipopolysaecharide were investigated. The absence of lipoprotein neither affects the rate of permeation of glucose 6-phosphate or of the β-lactam antibiotic eephsulodin through the PhoE pore nor the inhibition of cephsulodin permeation by polyphosphate. In contrast, heptose deficiency results in a 6- to 8-fold increase in the rates of permeation of glucose 6-phosphate and cephsulodin. Possible explanations for these data are discussed. It is argued that the lipopolysaecharide structure synthesized under phosphate limitation may be similar to that of the heptoseless mutant and hence that not only the structure of the PhoE protein pore but also the structure of the lipopolysaecharide may promote the uptake of Pi and Pi-containing solutes under phosphate limitation.